This invention relates generally to power supply selection, and more particularly to a processor system with power supply selection.
Introducing a new microprocessor to the market is easier if it operates in the systems built for a previous generation of microprocessors. Because of this, designers try to build their systems so that future, lower voltage microprocessors can be plugged in with a minimum of, and preferably no, redesign. That is, designers desire to have components which can support more than one generation of microprocessor voltage. A new generation microprocessor which uses a lower voltage may require a change in system components, unless efforts are taken to make the new processor compatible with existing components.
Implementing a new microprocessor which requires a different voltage supply for use in the system is currently dealt with in one of two manners. First, systems can be designed which are compatible with only a single generation of microprocessor. This eliminates any cross generation power supply concerns, but complicates the transition from one microprocessor to another. The second solution is to add a voltage regulator that can be switched between two different output voltages. This solution permits flexible motherboard the designs, but requires a more expensive voltage regulator module in the system.
In some systems, open drain signals may be used to alter the voltage between a processor and an interface chip. An open drain drive allows an interface chip to receive a high voltage that it needs to function without requiring the microprocessor to pull up to that high voltage. An open drain termination voltage may become too high for even an open drain output on the microprocessor to withstand. However, with recent processors the maximum voltage that can be tolerated using pull-up resisters for the open drain signals is below the minimum voltage at which the prior generation can operate.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a microprocessor system which allows the use of new processors while maintaining system voltage compatibility.
One embodiment of the present invention provides a processing system comprising a plurality of voltage regulation modules each having an output connection to supply an output voltage, and a microprocessor having a package, a plurality of external input connections and at least one external output connection. Each of the external input connections is connected to one of the output connections of the plurality of voltage regulation modules. An electrically conductive path is provided within the microprocessor package. The electrical connection is coupled to one of the plurality of external input connections and to at least one external output connection to selectively couple one of the output voltage supplies to a bus.
In another embodiment, a processing system motherboard comprises first and second voltage regulation modules each having an output connection to supply an output voltage, where the first voltage regulation module provides a voltage VCC 1, and the second voltage regulation module provides the voltage VCC 2. A microprocessor is provided which has a package, first and second external input connections and an external output connection. The first external input connection is connected to the output connection of the first voltage regulation module, and the second external input connection is connected to the output connection of the second voltage regulation module. An electrically conductive path is provided within the microprocessor package. The electrical connection is coupled to either the first or second external input connection and the external output connection to selectively couple either VCC 1 or VCC 2 to the external output connection. An open drain bus is coupled to the external output connection of the microprocessor, and peripheral circuitry coupled to the open drain bus.